Under the proposed approach, compliance requirements would vary based on age of the vehicle or engine being converted. EPA has found that the compliance process for older vehicles and engines could be streamlined, while maintaining environmental safeguards. As opposed to a one-size fits all approach, requirements would now be based on whether a vehicle or engine is deemed to be new, intermediate-age, or outside its expected useful life.

Conversion systems alter an existing vehicle or engine to enable it to run on a different type of fuel, such as switching a car to run on compressed natural gas. While properly engineered conversion systems can reduce or at least not increase emissions, poorly designed systems can lead to much more pollution. EPA reminds consumers only to use systems that have EPA approval.